Carbon monoxide (CO) is a common contaminant of refinery streams that can cause a variety of problems. Such problems can include deactivation of metal catalysts by poisoning and/or facilitating sintering on the catalyst, as well as safety and environmental concerns. In many instances, conventional removal of CO from refinery streams is accomplished by oxidation of the CO to form CO2, such as by exposing the CO to a catalyst including a noble metal supported on an amorphous oxide support. However, such catalysts are not selective for CO oxidation. As a result, unwanted side reactions can also occur that can result in loss of product yield and/or production of unwanted side products.
An example of an unwanted side reaction is the formation of NOx in the flue gas of a regenerator for a fluid catalytic cracking (FCC) system. CO is generated during the regeneration of FCC catalysts due to incomplete combustion of coke. To avoid emission of this CO to the atmosphere, the CO can be exposed to a noble metal catalyst to form CO2. Unfortunately, organic nitrogen-containing compounds are also present in the coke for an FCC catalyst. Such organic nitrogen-containing compounds are also oxidized by the noble metal catalyst, resulting in production of NOx. This NOx can potentially correspond to 90% of the NOx generated within a refinery. Such NOx can be converted to N2 via selective catalytic reduction, but performing this conversion requires addition of additional processing equipment to the regenerator flue stack and incurs substantial additional cost.
What is needed are improved systems and methods for removal of CO from refinery streams while reducing or minimizing additional equipment and/or costs for such removal. Additionally or alternately, what is needed are improved systems and methods for selective removal of C3− hydrocarbonaceous compounds, including alkanes, alkenes, alkynes, and/or alcohols, when such small hydrocarbonaceous compounds are present as impurities within a stream containing heavier hydrocarbonaceous compounds. In all of these scenarios, elimination of the smaller molecule(s) that may pose a problem while reducing or minimizing loss of desirable larger compounds is of interest.
U.S. Pat. Nos. 4,072,600 and 4,093,535 teach use of combustion-promoting metals such as Pt, Pd, Ir, Rh, Os, Ru and Re in cracking catalysts in concentrations of 0.01 to 50 ppm, based on total catalyst inventory. This type of approach can reduce or minimize CO concentration in regenerator flue gas, but can also result in production of substantial amounts of NOx.
U.S. Pat. No. 4,991,521 describes a regenerator where coke on spent FCC catalyst can be used to reduce NOx emissions from an FCC regenerator. The patent shows a two stage FCC regenerator, wherein flue gas from a second stage of regeneration contacts coked catalyst. Although effective at reducing NOx emissions, this approach cannot be used in most existing regenerators.
PCT Publication WO/2017/202495 describes synthetic zeolites comprising a catalytic metal, where the catalytic metal is (at least partially) encapsulated in a small pore zeolite structure.